There are many ways of transferring heat from one point or area to another point or area. Two examples of one kind of technology used today for transferring energy with a low thermal resistance from one point or area to another point or area are a heat pipe and a thermo siphon.
A heat pipe is a two-phase heat transfer device with an extremely high effective thermal conductivity. It can be cylindrical or planar, and the inner surface is lined with a capillary wicking material. The heat pipe is evacuated and back-filled with a small quantity of a working fluid such as water, acetone or methanol. Heat is absorbed in the evaporator region by vaporizing the working fluid. The vapour transports heat to the condenser region where the vapour condenses, releasing heat to the cooling medium such as air. The condensed working fluid is returned to the evaporator by gravity or by capillary action if working against gravity.
Heat pipes have a lower total thermal resistance than solid conductors, enabling them to transfer heat more efficiently and evenly. They are totally passive heat transfer systems, having no moving parts to wear out and requiring no energy to operate.
A thermo siphon is like the heat pipe a two-phase heat transfer device with an extremely high effective thermal conductivity. But the inner surface is not lined with a capillary wicking material and the thermo siphon will therefore only work by gravity. This means, that the condenser region has to be situated higher than the evaporator region.
The operating temperature range of both heat pipes and thermo siphons depends on the working fluid. In general, the units will transfer energy in a temperature range limited by the freezing point of the working fluid at low temperatures and the critical point of the working fluid at high temperatures. The thermal conductivity of the unit varies over temperature (depending on the working fluid).
At temperatures above the critical point, the unit will not transfer energy, as the gas will not condensate. The pressure of the gas, which depends of the temperature of the unit, will continue to increase at temperatures above the critical point of the working fluid.
As mentioned, the working fluid can be water, acetone, methanol, carbon dioxide or propanol, but other fluids can also be used.
In the system the condensator end of the thermo siphon or heat pipe is cooled by an active cooling device (for example compressor system, thermoelectric module or a Stirling cooler) and the evaporating end of the thermo siphon or heat pipe is used to cool a media (example metal block of dry-block calibrator or liquid of a liquid bath).